Vertebrate sight and human visual health depend upon the membranous architecture of rod and cone photoreceptor outer segments (OSs). A broad variety of sight-robbing diseases is associated with defects in OS architecture; however, neither the underlying disease etiologies, nor the fundamental biology of the receptor cells is well understood. In particular, the molecular mechanisms responsible for generating and stabilizing the structure of mature rod and cone OS disks are not yet known. The long-term goal of this research is to define OS architecture and renewal in sufficient detail to explain how defects generate retinal disease and design effective therapeutic strategies. The current goal is to determine how peripherin-2/rds (P/rds) functions as an organizer for OS membranes. This integral membrane tetraspanin acts in an essential, though mechanistically uncertain fashion to support OS architecture for both rods and cones, and inherited mutations in P/rds cause a broad range of progressive diseases, including retinitis pigmentosa and macular degenerations. The first Aim of this study will determine the importance of known protein structural/regulatory determinants for P/rds induction of highly curved membranes. The second Aim will test the hypothesis that the P/rds C-terminus is normally membrane associated via partitioning of an inducible amphipathic helix that can function to tether OS disk rims together. The third Aim will test the hypothesis that pathogenic mutations in the P/rds C-terminal domain can preferentially impact cone photoreceptors. Successful completion of the work proposed would improve knowledge of P/rds protein structure-function, clarify how P/rds can generate high curvature membranes to form and stabilize OS disks, and would provide a mechanistic basis for understanding how pathogenic mutations in P/rds preferentially affect cone (vs. rod) photoreceptors. The work could also make a positive impact by suggesting new strategies for managing progressive retinal degenerations that result from primary pathologies in OS structure.